A front set of chain sprockets used in a bicycle comprises two or three chain sprockets which drive a chain that further transmits pedaling power to chain sprockets mounted on an axle in a rear bicycle wheel. Since each of the front sprockets has a different number of teeth, they enable different rotating speeds of the rear sprockets and thereby provide different bicycle driving speeds. In order to change driving ratios the chain has to be replaced from one sprocket to another by a derailleur which is mounted proximate to the front chain sprockets.
The sprockets have significantly different diameters which, in turn, makes the chain replacement relatively abrupt and difficult. Even the most sophisticated derailleurs cannot provide smooth shifting and eliminate the related stress and power loss. Every time the chain is displaced from one sprocket and mounted on another sprocket it causes an interruption of power flow and related loss of pedaling power.
It is an object of the present invention to provide a device which will enable an uninterrupted flow of pedaling power from a crankshaft to a drive chain of a bicycle or similar pedal propelled vehicles. The present invention comprises a rotor assembly wherein three members are provided within the front chain sprocket of the bicycle and mounted in a manner which enables all of them to work in concert with each other. An inner rotor is located within a middle rotor and the middle rotor is located within an outer rotor. The inner rotor has a certain number of lobes while the inner opening of the middle rotor has a certain higher number of pockets which receive the lobes during the rotation. The middle rotor also has a certain number of lobes on its outer circumference while the outer rotor""s inner opening has a certain higher number of pockets which receive the lobes of the middle rotor.
The inner rotor and the outer rotor rotate around the same axis while the middle rotor rotates around a different axis. This enables the middle rotor to rotate eccentrically with respect to the inner and outer rotors which, in turn, enables the middle rotor to transfer the rotating force between the inner and outer rotors. The inner and outer rotor rotate around the same axis as the front chain sprocket which rotates around the outer rotor. An overrunning clutch connects the inner rotor to the bicycle crankshaft and this rotor serves as a power input member during the slowest speed. The inner rotor is also directly connected to the chain sprocket by mechanical means to serve as the power transfer member during the fastest speed, as explained later in this specification. The outer rotor is by mechanical means also connected to the bicycle crankshaft and serves as an input member during the 2nd and 3rd speed.
According to the process of the invention, when the inner rotor is pushed by the rotational force of the crankshaft, its lobes exert force onto the pockets inside the middle rotor and force the middle rotor to rotate in the same direction but at a slower speed. Further, the middle rotor""s lobes force the outer rotor to rotate in the same direction at a lower speed. The rotating force of the outer rotor is over an overrunning clutch further transmitted onto the chain sprocket. Since the inner rotor has less lobes than the pockets in the middle rotor and the middle rotor has less lobes than the pockets in the outer rotor, the outer rotor rotates at the rate defined by the difference between the lobes and the pockets in all rotors. The rotating speed of the outer rotor is slower than the rotating speed of both other rotors and this speed of the outer rotor corresponds to the slowest possible rotating speed, hereinafter referred to as the xe2x80x9c1st speedxe2x80x9d.
When the outer rotor is connected to the crankshaft, the overrunning clutch which connects the inner rotor to the crankshaft is disconnected and the sprocket is (over the overrunning clutch) forced to rotate at the speed of the outer rotor which equals the rotating speed of the crankshaft. The obtained rotating speed is faster and hereinafter referred to as the xe2x80x9c2nd speedxe2x80x9d. During the time when the outer rotor is firmly connected to the crankshaft, the inner rotor rotates at a faster rate with respect to the outer rotor. When the inner rotor is directly connected to the sprocket while the outer rotor is connected to the crankshaft, the rotating speed of the sprocket equals the rotating speed of the inner rotor and the sprocket is forced to rotate at the fastest possible rate, hereinafter referred to as the xe2x80x9c3rd speedxe2x80x9d.
The present invention provides a few different versions of a speed changing device which can be used on bicycles or similar pedal-propelled vehicles. The versions presented in this specification include these which provide 3 output speeds and these which provide 2 output speeds. All versions operate apply the same operating principles wherein the change in output rotating speeds is obtained by alternately providing different connections between the crankshaft, rotors, and chain sprocket and wherein the different number of the rotors"" lobes and pockets results in different rotating ratios of the rotors. The features and advantages of the present invention will become apparent from the following brief description of the drawings and a detailed description of the invention.